Twin scroll turbocharger configurations may be used in turbocharged engines. A twin scroll turbocharger configuration may separate an inlet to an exhaust turbine into two separate passages connected to exhaust manifold runners so that exhaust from engine cylinders whose exhaust gas pulses may interfere with each other are separated.
For example, on a typical inline four (I4) engine with a cylinder firing order of 1-3-4-2, exhaust manifold runners from cylinder 1 and cylinder 4 may be connected to a first inlet of a twin scroll turbine and exhaust manifold runners from cylinder 2 and cylinder 3 may be connected to a second inlet of said twin scroll turbine, where the second inlet is different from the first inlet. Separating exhaust gas pulses in this way may result in increased efficiency of exhaust gas delivery to the turbine and may increase power output of the turbine.
However, the above configuration may not be applicable to an engine with a different firing order. As an example, ignition events in a four-cylinder engine may be configured to occur in the following order: 1-3-2-4. In this scenario, coupling exhaust manifold runners from cylinders 1 and 4 to a first inlet and coupling exhaust runners from cylinders 2 and 3 to a second inlet of the twin scroll turbine may result in exhaust pulse interference producing a decrease in volumetric efficiency and affecting turbine spool-up.
The inventors herein have identified the above issue and devised an approach that partially addresses this issue. In one approach, a method for the engine comprises directing exhaust from a first outer cylinder and a first inner cylinder of four cylinders to a first scroll of a twin scroll turbocharger, directing exhaust from a second outer cylinder and a second inner cylinder of the four cylinders to a second scroll of the twin scroll turbocharger, and during a first condition, operating all cylinders with at least one uneven firing. An example engine may comprise four cylinders arranged in an inline configuration with a firing order of 1-3-2-4, as mentioned above. Based on cylinder positions within an engine block, cylinder 1 may be categorized as a first outer cylinder, cylinder 4 may be identified as a second outer cylinder, cylinder 2 may be categorized as a first inner cylinder (next to cylinder 1), and cylinder 3 may be identified based on its position in the engine block as second inner cylinder (next to cylinder 4). By separating exhaust from cylinders 1 and 2 from exhaust flowing out of cylinders 3 and 4, exhaust pulse separation may be maintained between cylinders 1 and 4, and between cylinders 2 and 3.
As another example, a turbocharged variable displacement engine may include four inline cylinders such that two cylinders are positioned as outer cylinders while remaining two cylinders are positioned as inner cylinders. The engine may be configured to operate with a firing sequence of first outer cylinder-second inner cylinder-second outer cylinder-first inner cylinder. To enable sufficient exhaust pulse separation, exhaust runners from the first outer cylinder and the first inner cylinder may be fluidically coupled to a first scroll of an exhaust turbine of the turbocharger while exhaust runners from the second inner cylinder and the second outer cylinder may be fluidically coupled to a second scroll of the exhaust turbine of the turbocharger. The engine be operated with uneven firing by firing the first outer cylinder midway between the second inner cylinder and the second outer cylinder, and by firing the first inner cylinder, the second inner cylinder, and the second outer cylinder at 240 crank angle degree intervals from each other. Thus, the first outer cylinder may be fired approximately 120 crank angle degrees after the second outer cylinder has fired, and 120 crank angle degrees before the second inner cylinder fires. The engine may also be operated in a variable displacement mode (or reduced cylinder mode) by deactivating the first outer cylinder and firing the remaining three cylinders at 240 crank angle degree intervals.
In this way, a turbocharged engine with a firing order of 1-3-2-4 may be operated with exhaust pulse separation. By delivering exhaust from cylinder 1 and cylinder 2 to a first scroll of an exhaust turbine and directing exhaust from cylinder 3 and cylinder 4 to a second scroll of the exhaust turbine, exhaust pulse interference during an uneven firing mode may be reduced. Each scroll of the exhaust turbine may receive exhaust pulses separated by a minimum of 240 crank angle degrees in the full-cylinder mode with uneven firing and the reduced cylinder even firing mode. Exhaust pulse separation with a twin scroll turbocharger may enable more efficient recovery of kinetic energy from the exhaust gases. Therefore, the engine may operate with increased power output and improved fuel efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.